1. Field of the Invention
The present invention relates generally to minimally invasive methods, devices and systems for treating spinal disorders using imaging guidance. More particularly, the present invention relates to devices and methods to reduce stenosis and increase the cross-sectional area of the spinal canal available for the spinal cord. Still more particularly, the present invention relates to devices and methods to percutaneously excise portions of an enlarged ligamentum flavum.
2. Background of the Invention
The vertebral column (spine, spinal column, backbone) forms the main part of the axial skeleton, provides a strong yet flexible support for the head and body, and protects the spinal cord disposed in the vertebral canal, which is formed within the vertebral column. The vertebral column comprises a stack of vertebrae with an intervertebral disc between adjacent vertebrae. The vertebrae are stabilized by muscles and ligaments that hold the vertebrae in place and limit the movements of the vertebrae.
As illustrated in FIG. 1, each vertebra 10 includes a vertebral body 12 that supports a vertebral arch 14. A median plane 210 generally divides vertebra 10 into two substantially equal lateral sides. Vertical body 12 has the general shape of a short cylinder and is anterior to the vertebral arch 14. The vertebral arch 14 together with vertebral body 12 encloses a space termed the vertebral foramen 15. The succession of vertebral foramen 15 in adjacent vertebrae 10 along the vertebral column define the vertebral canal (spinal canal), which contains the spinal cord.
Vertebral arch 14 is formed by two pedicles 24 which project posteriorly to meet two laminae 16. The two laminae 16 meet posteriomedially to form the spinous process 18. At the junction of pedicles 24 and laminae 16, six processes arise. Two transverse processes 20 project posterolaterally, two superior articular processes 22 project generally superiorly and are positioned superior to two inferior articular processes 25 that generally project inferiorly.
The vertebral foramen 15 is generally an oval shaped space that contains and protects the spinal cord 28. Spinal cord 28 comprises a plurality of nerves 34 surrounded by cerebrospinal fluid (CSF) and an outermost sheath/membrane called the dural sac 32. The CSF filled dural sac 32 containing nerves 34 is relatively compressible. Posterior to the spinal cord 28 within vertebral foramen 15 is the ligamentum flavum 26. Laminae 16 of adjacent vertebral arches 14 in the vertebral column are joined by the relatively broad, elastic ligamentum flavum 26.
In degenerative conditions of the spine, narrowing of the spinal canal (stenosis) can occur. Lumbar spinal stenosis is often defined as a dural sac cross-sectional area less than 100 mm2 or an anterior-posterior (AP) dimension of the canal of less than 10-12 mm for an average male.
The source of many cases of lumbar spinal stenosis is thickening of the ligamentum flavum. Spinal stenosis may also be caused by subluxation, facet joint hypertrophy, osteophyte formation, underdevelopment of spinal canal, spondylosis deformans, degenerative intervertebral discs, degenerative spondylolisthesis, degenerative arthritis, ossification of the vertebral accessory ligaments and the like. A less common cause of spinal stenosis, which usually affects patients with morbid obesity or patients on oral corticosteroids, is excess fat in the epidural space. The excessive epidural fat compresses the dural sac, nerve roots and blood vessels contained therein, resulting in back and leg pain and weakness and numbness of the legs. Spinal stenosis may also affect the cervical and, less commonly, the thoracic spine.
Patients suffering from spinal stenosis are typically first treated with exercise therapy, analgesics, and anti-inflammatory medications. These conservative treatment options frequently fail. If symptoms are severe, surgery is required to decompress the spinal cord and nerve roots.
In some conventional approaches to correct stenosis in the lumbar region, an incision is made in the back and the muscles and supporting structures are stripped away from the spine, exposing the posterior aspect of the vertebral column. The thickened ligamentum flavum is then exposed by removal of a portion of the vertebral arch, often at the laminae, covering the back of the spinal canal (laminectomy). The thickened ligamentum flavum ligament can then be excised by sharp dissection with a scalpel or punching instruments such as a Kerison punch that is used to remove small chips of tissue. The procedure is performed under general anesthesia. Patients are usually admitted to the hospital for approximately five to seven days depending on the age and overall condition of the patient. Patients usually require between six weeks and three months to recover from the procedure. Further, many patients need extended therapy at a rehabilitation facility to regain enough mobility to live independently.
Much of the pain and disability after an open laminectomy results from the tearing and cutting of the back muscles, blood vessels, supporting ligaments, and nerves that occurs during the exposure of the spinal column. Also, because the spine stabilizing back muscles and ligaments are stripped and detached from the spine during the laminectomy, these patients frequently develop spinal instability post-operatively.
Minimally invasive techniques offer the potential for less post-operative pain and faster recovery compared to traditional open surgery. Percutaneous interventional spinal procedures can be performed with local anesthesia, thereby sparing the patient the risks and recovery time required with general anesthesia. In addition, there is less damage to the paraspinal muscles and ligaments with minimally invasive techniques, thereby reducing pain and preserving these important stabilizing structures.
Various techniques for minimally invasive treatment of the spine are known. Microdiscectomy is performed by making a small incision in the skin and deep tissues to create a portal to the spine. A microscope is then used to aid in the dissection of the adjacent structures prior to discectomy. The recovery for this procedure is much shorter than traditional open discectomies. Percutaneous discectomy devices with fluoroscopic guidance have been used successfully to treat disorders of the disc but not to treat spinal stenosis or the ligamentum flavum directly. Arthroscopy or direct visualization of the spinal structures using a catheter or optical system have also been proposed to treat disorders of the spine including spinal stenosis, however these devices still use miniaturized standard surgical instruments and direct visualization of the spine similar to open surgical procedures. These devices and techniques are limited by the small size of the canal and these operations are difficult to perform and master. In addition, these procedures are painful and often require general anesthesia. Further, the arthroscopy procedures are time consuming and the fiber optic systems are expensive to purchase and maintain.
Still further, because the nerves of the spinal cord pass through the spinal canal directly adjacent to and anterior to the ligamentum flavum, any surgery, regardless of whether open or percutaneous, includes a risk of damage to the nerves of the spinal cord.
Hence, it remains desirable to provide simple methods, techniques, and devices for treating spinal stenosis and other spinal disorders without requiring open surgery. It is further desired to provide a system whereby the risk of damage to the dural sac containing the spinal nerves may be reduced.